Re: [PATCH 2/8] fwctl: Basic ioctl dispatch for the character device

Przemek Kitszel
2024-06-05T15:43:03Z

On 6/3/24 17:53, Jason Gunthorpe wrote:
> Each file descriptor gets a chunk of per-FD driver specific context that
> allows the driver to attach a device specific struct to. The core code
> takes care of the memory lifetime for this structure.
>
> The ioctl dispatch and design is based on what was built for iommufd. The
> ioctls have a struct which has a combined in/out behavior with a typical
> 'zero pad' scheme for future extension and backwards compatibility.

I would go one step further and introduce a new syscall, that would
smooth out typical problems of ioctl, and base it on some TLV scheme
(similar to netlink, in some kind a way smaller brother of protobuf).
Perhaps with the name more broad than fw-knob-tuning.

Then I would go two steps back and a driver layer to interpert those
syscalls to have at least some sort of openness.

>
> Like iommufd some shared logic does most of the ioctl marshalling and
> compatibility work and tables diatches to some function pointers for
> each unique iotcl.
>
> This approach has proven to work quite well in the iommufd and rdma
> subsystems.
>
> Allocate an ioctl number space for the subsystem.
>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
> .../userspace-api/ioctl/ioctl-number.rst | 1 +
> MAINTAINERS | 1 +
> drivers/fwctl/main.c | 124 +++++++++++++++++-
> include/linux/fwctl.h | 31 +++++
> include/uapi/fwctl/fwctl.h | 41 ++++++
> 5 files changed, 196 insertions(+), 2 deletions(-)
> create mode 100644 include/uapi/fwctl/fwctl.h
>
> diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst
> index a141e8e65c5d3a..4d91c5a20b98c8 100644
> --- a/Documentation/userspace-api/ioctl/ioctl-number.rst
> +++ b/Documentation/userspace-api/ioctl/ioctl-number.rst
> @@ -324,6 +324,7 @@ Code Seq# Include File Comments
> 0x97 00-7F fs/ceph/ioctl.h Ceph file system
> 0x99 00-0F 537-Addinboard driver
> <mailto:buk@buks.ipn.de>
> +0x9A 00-0F include/uapi/fwctl/fwctl.h
> 0xA0 all linux/sdp/sdp.h Industrial Device Project
> <mailto:kenji@bitgate.com>
> 0xA1 0 linux/vtpm_proxy.h TPM Emulator Proxy Driver
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 833b853808421e..94062161e9c4d7 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -9084,6 +9084,7 @@ S: Maintained
> F: Documentation/userspace-api/fwctl.rst
> F: drivers/fwctl/
> F: include/linux/fwctl.h
> +F: include/uapi/fwctl/
>
> GALAXYCORE GC0308 CAMERA SENSOR DRIVER
> M: Sebastian Reichel <sre@kernel.org>
> diff --git a/drivers/fwctl/main.c b/drivers/fwctl/main.c
> index ff9b7bad5a2b0d..7ecdabdd9dcb1e 100644
> --- a/drivers/fwctl/main.c
> +++ b/drivers/fwctl/main.c
> @@ -9,26 +9,131 @@
> #include <linux/container_of.h>
> #include <linux/fs.h>
>
> +#include <uapi/fwctl/fwctl.h>
> +
> enum {
> FWCTL_MAX_DEVICES = 256,
> };
> static dev_t fwctl_dev;
> static DEFINE_IDA(fwctl_ida);
>
> +struct fwctl_ucmd {
> + struct fwctl_uctx *uctx;
> + void __user *ubuffer;
> + void *cmd;
> + u32 user_size;
> +};
> +
> +/* On stack memory for the ioctl structs */
> +union ucmd_buffer {
> +};
> +
> +struct fwctl_ioctl_op {
> + unsigned int size;
> + unsigned int min_size;
> + unsigned int ioctl_num;
> + int (*execute)(struct fwctl_ucmd *ucmd);
> +};
> +
> +#define IOCTL_OP(_ioctl, _fn, _struct, _last) \
> + [_IOC_NR(_ioctl) - FWCTL_CMD_BASE] = { \
> + .size = sizeof(_struct) + \
> + BUILD_BUG_ON_ZERO(sizeof(union ucmd_buffer) < \
> + sizeof(_struct)), \
> + .min_size = offsetofend(_struct, _last), \
> + .ioctl_num = _ioctl, \
> + .execute = _fn, \
> + }
> +static const struct fwctl_ioctl_op fwctl_ioctl_ops[] = {
> +};
> +
> +static long fwctl_fops_ioctl(struct file *filp, unsigned int cmd,
> + unsigned long arg)
> +{
> + struct fwctl_uctx *uctx = filp->private_data;
> + const struct fwctl_ioctl_op *op;
> + struct fwctl_ucmd ucmd = {};
> + union ucmd_buffer buf;
> + unsigned int nr;
> + int ret;
> +
> + nr = _IOC_NR(cmd);
> + if ((nr - FWCTL_CMD_BASE) >= ARRAY_SIZE(fwctl_ioctl_ops))
> + return -ENOIOCTLCMD;
> + op = &fwctl_ioctl_ops[nr - FWCTL_CMD_BASE];
> + if (op->ioctl_num != cmd)
> + return -ENOIOCTLCMD;
> +
> + ucmd.uctx = uctx;
> + ucmd.cmd = &buf;
> + ucmd.ubuffer = (void __user *)arg;
> + ret = get_user(ucmd.user_size, (u32 __user *)ucmd.ubuffer);
> + if (ret)
> + return ret;
> +
> + if (ucmd.user_size < op->min_size)
> + return -EINVAL;
> +
> + ret = copy_struct_from_user(ucmd.cmd, op->size, ucmd.ubuffer,
> + ucmd.user_size);
> + if (ret)
> + return ret;
> +
> + guard(rwsem_read)(&uctx->fwctl->registration_lock);
> + if (!uctx->fwctl->ops)
> + return -ENODEV;
> + return op->execute(&ucmd);
> +}
> +
> static int fwctl_fops_open(struct inode *inode, struct file *filp)
> {
> struct fwctl_device *fwctl =
> container_of(inode->i_cdev, struct fwctl_device, cdev);
> + struct fwctl_uctx *uctx __free(kfree) = NULL;
> + int ret;
> +
> + guard(rwsem_read)(&fwctl->registration_lock);
> + if (!fwctl->ops)
> + return -ENODEV;
> +
> + uctx = kzalloc(fwctl->ops->uctx_size, GFP_KERNEL | GFP_KERNEL_ACCOUNT);
> + if (!uctx)
> + return -ENOMEM;
> +
> + uctx->fwctl = fwctl;
> + ret = fwctl->ops->open_uctx(uctx);
> + if (ret)
> + return ret;
> +
> + scoped_guard(mutex, &fwctl->uctx_list_lock) {
> + list_add_tail(&uctx->uctx_list_entry, &fwctl->uctx_list);
> + }
>
> get_device(&fwctl->dev);
> - filp->private_data = fwctl;
> + filp->private_data = no_free_ptr(uctx);
> return 0;
> }
>
> +static void fwctl_destroy_uctx(struct fwctl_uctx *uctx)
> +{
> + lockdep_assert_held(&uctx->fwctl->uctx_list_lock);
> + list_del(&uctx->uctx_list_entry);
> + uctx->fwctl->ops->close_uctx(uctx);
> +}
> +
> static int fwctl_fops_release(struct inode *inode, struct file *filp)
> {
> - struct fwctl_device *fwctl = filp->private_data;
> + struct fwctl_uctx *uctx = filp->private_data;
> + struct fwctl_device *fwctl = uctx->fwctl;
>
> + scoped_guard(rwsem_read, &fwctl->registration_lock) {
> + if (fwctl->ops) {
> + guard(mutex)(&fwctl->uctx_list_lock);
> + fwctl_destroy_uctx(uctx);
> + }
> + }
> +
> + kfree(uctx);
> fwctl_put(fwctl);
> return 0;
> }
> @@ -37,6 +142,7 @@ static const struct file_operations fwctl_fops = {
> .owner = THIS_MODULE,
> .open = fwctl_fops_open,
> .release = fwctl_fops_release,
> + .unlocked_ioctl = fwctl_fops_ioctl,
> };
>
> static void fwctl_device_release(struct device *device)
> @@ -46,6 +152,7 @@ static void fwctl_device_release(struct device *device)
>
> if (fwctl->dev.devt)
> ida_free(&fwctl_ida, fwctl->dev.devt - fwctl_dev);
> + mutex_destroy(&fwctl->uctx_list_lock);
> kfree(fwctl);
> }
>
> @@ -69,6 +176,9 @@ _alloc_device(struct device *parent, const struct fwctl_ops *ops, size_t size)
> return NULL;
> fwctl->dev.class = &fwctl_class;
> fwctl->dev.parent = parent;
> + init_rwsem(&fwctl->registration_lock);
> + mutex_init(&fwctl->uctx_list_lock);
> + INIT_LIST_HEAD(&fwctl->uctx_list);
> device_initialize(&fwctl->dev);
> return_ptr(fwctl);
> }
> @@ -134,8 +244,18 @@ EXPORT_SYMBOL_NS_GPL(fwctl_register, FWCTL);
> */
> void fwctl_unregister(struct fwctl_device *fwctl)
> {
> + struct fwctl_uctx *uctx;
> +
> cdev_device_del(&fwctl->cdev, &fwctl->dev);
>
> + /* Disable and free the driver's resources for any still open FDs. */
> + guard(rwsem_write)(&fwctl->registration_lock);
> + guard(mutex)(&fwctl->uctx_list_lock);
> + while ((uctx = list_first_entry_or_null(&fwctl->uctx_list,
> + struct fwctl_uctx,
> + uctx_list_entry)))
> + fwctl_destroy_uctx(uctx);
> +
> /*
> * The driver module may unload after this returns, the op pointer will
> * not be valid.
> diff --git a/include/linux/fwctl.h b/include/linux/fwctl.h
> index ef4eaa87c945e4..1d9651de92fc19 100644
> --- a/include/linux/fwctl.h
> +++ b/include/linux/fwctl.h
> @@ -11,7 +11,20 @@
> struct fwctl_device;
> struct fwctl_uctx;
>
> +/**
> + * struct fwctl_ops - Driver provided operations
> + * @uctx_size: The size of the fwctl_uctx struct to allocate. The first
> + * bytes of this memory will be a fwctl_uctx. The driver can use the
> + * remaining bytes as its private memory.
> + * @open_uctx: Called when a file descriptor is opened before the uctx is ever
> + * used.
> + * @close_uctx: Called when the uctx is destroyed, usually when the FD is
> + * closed.
> + */
> struct fwctl_ops {
> + size_t uctx_size;
> + int (*open_uctx)(struct fwctl_uctx *uctx);
> + void (*close_uctx)(struct fwctl_uctx *uctx);
> };
>
> /**
> @@ -26,6 +39,10 @@ struct fwctl_device {
> struct device dev;
> /* private: */
> struct cdev cdev;
> +
> + struct rw_semaphore registration_lock;
> + struct mutex uctx_list_lock;
> + struct list_head uctx_list;
> const struct fwctl_ops *ops;
> };
>
> @@ -65,4 +82,18 @@ DEFINE_FREE(fwctl, struct fwctl_device *, if (_T) fwctl_put(_T));
> int fwctl_register(struct fwctl_device *fwctl);
> void fwctl_unregister(struct fwctl_device *fwctl);
>
> +/**
> + * struct fwctl_uctx - Per user FD context
> + * @fwctl: fwctl instance that owns the context
> + *
> + * Every FD opened by userspace will get a unique context allocation. Any driver
> + * private data will follow immediately after.
> + */
> +struct fwctl_uctx {
> + struct fwctl_device *fwctl;
> + /* private: */
> + /* Head at fwctl_device::uctx_list */
> + struct list_head uctx_list_entry;
> +};
> +
> #endif
> diff --git a/include/uapi/fwctl/fwctl.h b/include/uapi/fwctl/fwctl.h
> new file mode 100644
> index 00000000000000..0bdce95b6d69d9
> --- /dev/null
> +++ b/include/uapi/fwctl/fwctl.h
> @@ -0,0 +1,41 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/* Copyright (c) 2024, NVIDIA CORPORATION & AFFILIATES.
> + */
> +#ifndef _UAPI_FWCTL_H
> +#define _UAPI_FWCTL_H
> +
> +#include <linux/types.h>
> +#include <linux/ioctl.h>
> +
> +#define FWCTL_TYPE 0x9A
> +
> +/**
> + * DOC: General ioctl format
> + *
> + * The ioctl interface follows a general format to allow for extensibility. Each
> + * ioctl is passed in a structure pointer as the argument providing the size of
> + * the structure in the first u32. The kernel checks that any structure space
> + * beyond what it understands is 0. This allows userspace to use the backward
> + * compatible portion while consistently using the newer, larger, structures.
> + *
> + * ioctls use a standard meaning for common errnos:
> + *
> + * - ENOTTY: The IOCTL number itself is not supported at all
> + * - E2BIG: The IOCTL number is supported, but the provided structure has
> + * non-zero in a part the kernel does not understand.
> + * - EOPNOTSUPP: The IOCTL number is supported, and the structure is
> + * understood, however a known field has a value the kernel does not
> + * understand or support.
> + * - EINVAL: Everything about the IOCTL was understood, but a field is not
> + * correct.
> + * - ENOMEM: Out of memory.
> + * - ENODEV: The underlying device has been hot-unplugged and the FD is
> + * orphaned.
> + *
> + * As well as additional errnos, within specific ioctls.
> + */
> +enum {
> + FWCTL_CMD_BASE = 0,
> +};
> +
> +#endif